1. Field of the Invention
The present invention relates to immunoassays for determining and detecting the presence of immunologically reactive analytes in aqueous samples and in particular to self contained, single step, solid phase strip form assay devices and methodology.
2. Prior Activities and the State of the Art
Assays based on reactions between specifically immunoreactive substances are used extensively today in fields such as clinical medicine, forensic medicine, environmental testing, food quality assurance, drug testing and other related areas for detecting the presence of immunoreactive analytes in test samples.
The development of non-radioactive labels or markers has facilitated the use of immunoassay diagnostic procedures outside of laboratory settings and in remote sites such as physician's offices and even the homes of the users. In the physician's office, immunological procedures are useful for providing rapid, simple assays which may be performed while the patient is still in the office so that the diagnosis can be accomplished without delay and treatment instituted during a single visit. Without such simple assays, it was often necessary for the physician to collect a sample from a patient during a first visit and to have the sample analyzed by a clinical laboratory with the results reported back to the physician by the laboratory at a later time. In the meanwhile, the patient was sent home and was required to return for a second visit with the physician in order to receive appropriate treatment and/or medication. Manifestly, such delay was inefficient and inappropriate and in some cases even be life threatening.
Home testing has become desirable to facilitate testing by the consumer in the privacy of his or her own home. The results of such testing might, for example, indicate the necessity or lack of necessity of a visit to the physician. Examples of useful tests for the "at home" market include tests for pregnancy, ovulation, streptococcus infection and other infections which ar detectable by analysis of body fluids such as urine, saliva, throat fluids, pus, vaginal fluids, blood or other appropriate test samples.
For remote site testing, assuming appropriate sensitivity and specificity can be achieved, there are at least three other requirements for practical assay procedures. The first of these desirable factors is speed in that the assay must be performed in an acceptably short period of time, the shorter the better. Stability is also a desirable feature in that the components of the assay should be stable for an extended period of time without refrigeration or special handling. Finally, from a commercial view point it is desirable that the test be convenient to use and as simple as possible requiring only minimal or n instrumentation and precluding mistakes and poor performance resulting in incorrect interpretations.
One of the difficulties encountered in the development of test devices for remote site testing is the provision of a practical pre-packaged disposable device to facilitate efficient, relatively inexpensive, fool proof test procedures. This, of course, requires a device which is inexpensive to construct, which has a shelf life appropriate to the commercial use of the device, which is protected against contamination during handling, which may be simply and conveniently utilized when the appropriate time arises, and which may conveniently and safely be used by even untrained persons.
The device illustrated in U.S. Pat. No. 4,868,108 addresses some of these problems; however, this device incorporates a test which utilizes enzyme color formers that depend on the presence of substrates and are often unstable and adversely influence shelf life. The '108 patent is commonly assigned and the entirety of the disclosure thereof is hereby specifically incorporated by reference.
Another known device is disclosed in U.K. Patent Application G.B. 2204398A. This device uses colloidal gold or colored particles as so called "direct" labels; however, in this device the non-labelled reaction component is permanently immobilized at the observation zone. This effects the efficiency of the analyte detection mechanism.
These prior devices leave unsatisfied the need for a simple inexpensive, efficient, fool proof, pre-packaged, one step device that has good shelf life characteristics.